Pet chews and snacks can be manufactured by treating byproducts from cattle and other animals to produce hardened substances which resemble bone and are enjoyable and healthful for pets to chew on. The pet chew manufacturing industry has long sought an efficient method for manufacturing pet chews which results in a substantially pure rawhide product,(i.e., without the disadvantages of substantial fillers, as detailed below) allows the addition of various flavorings, colorings and other additives and enables the configuration of the pet chew in various shapes and sizes that are attractive to the pet and the pet owner.
It has also long been desired to achieve a rawhide pet chew product by utilizing rawhide scraps, which are the by-products of the manufacture of other rawhide products. Often the scraps amount to 50% of the total output, yet today must be discarded as waste or used in a much less valuable fashion, such as glue manufacture. The scraps are often chemically treated and present disposal problems. A process for utilizing rawhide scraps would save money and minimize waste.
Rawhide is a byproduct of the slaughter of hoofed animals and consists of the hide, tendons etc. of the animal. Rawhide contains about 65-70% water, 30-35% dry material and less than 1% ash. The dry material is largely made up of fibrous proteins, collagen, keratin, elastin and reticulin. Due to this high water content, previously known methods of processing rawhide required that the rawhide be dried before it is used to produce pet chews.
Early methods of manufacturing pet chews out of substantially pure rawhide are as simple as preparing and drying rawhide strips until they are hard and bonelike. These nonmechanical methods consist of preparing the rawhide by removing, either chemically or otherwise, the fat and hair found on the cattle ligaments and other material which comprise the raw starting material. The treated rawhide is then cut and rolled into the desired shape, such as a rope or strip and dried. Coloring and flavor additives are applied to the chew by coating the outside of the rawhide strip once dry.
One of the simple methods requires drying the cut rawhide in the sun, before the rolling step, in order to preserve the rawhide. Prior to the rolling process, the dried rawhide is dipped in water, making it soft and easier to roll. The rawhide therefore needs very little drying once rolled. However, this drying process results in yellow or brown bones which are unappealing to pets and their owners.
Another nonmechanical method consists of working with the rawhide in the wet state, possibly wringing them out before processing. The rawhide is cut and rolled in the wet state.
The nonmechanical "clean, cut and dry" methods of producing pet chews are unsatisfactory since they are labor and energy intensive and time consuming. The methods are labor intensive because the treated skins are sorted depending on their size, laid out, cut into big strips, distributed to the workers who roll them into bones, placed on trays, shipped to the ovens and turned over once a day until dry. There are also problems with quality control. Because of all the manual work involved, the percentage of `seconds` and rejects is unreasonably high when compared to machine made products.
These methods are energy intensive because the rawhide has to be dried slowly once rolled to obtain a hard (15% moisture content) product. Slow drying is necessary because of the risk of cooking the rolled product into gelatin. Typically the drying process can last up to 15-20 days, starting off with a very low temperature (approximately 50.degree. C.) and gradually reaching 80.degree. C. The drying involves electric fans and wood heated air, turning 24 hours a day.
Further, the addition of additives is limited or not feasible through these methods. Coating the outside of the strip is unsatisfactory since there is no way to disperse the additive throughout the remainder of the chew. Also, it is difficult to mold the rawhide strip so it mimics natural bone or other shapes attractive to pets and their owners.
Illustrative of the above discussed nonmechanical method for manufacturing rawhide chews is U.S. Pat. No. 5,149,550 to Mohilef (1992), which teaches the manufacture of pet chews by (i) washing ligaments from cattle and other hoofstock in an aqueous degreasing solution or roasting, thereby rendering the ligaments substantially free of fat, and (ii) drying until hard.
U.S. Pat. No. 5,047,231 to Spanier et al., (1991) discloses a process for preparing rawhide by adding an inorganic pyrophosphate compound to rawhide strips and then drying the rawhide. The resultant pyrophosphate coated product, when chewed by the dog, results in reduced tartar accumulation on the dog's teeth.
Since the nonmechanical method of producing rawhide pet chews failed to satisfy the industry needs, the art turned to mechanical methods of manufacturing pet chews from rawhide. One mechanical method is to mechanically grind the rawhide fibers or the rawhide starting material. However, this method has failed to provide a solution since in order to mold the rawhide fibers after grinding it is necessary to add a filler, such as flour, starch or gelatin, to bind the rawhide fibers together.
A pet chew which is part filler fails to satisfy a pet since it will come apart in the pet's mouth. In comparison, a substantially pure rawhide pet treat will last much longer than a treat consisting of rawhide and fillers. The whole point about rawhide bones is (a) they have a natural appealing taste, and (b) they are hard enough to chew for a long time. The reason rawhide chews last for a long time is that they are all one piece and not lots of little crumbs glued together with fillers, such as gelatin or starch, which are easily dissolvable in dog saliva. Mechanical methods have never been able to reconstruct the rawhide's consistency because of the necessity of fillers.
U.S. Pat. No. 4,260,635 to Fisher (1981), discloses an example of a mechanical method of processing rawhide treats that requires filler. Fisher discloses a food system product consisting of multiple layers of pet food and supporting fibers, including cellulose or rawhide. Fisher teaches treating cattle skin or other skin parts and then grinding them into meal. The meal is combined with an appropriate binder, such as starch, and then the mixture is molded into a suitable shape. The molded shapes are subsequently subjected to pressure or a combination of pressure and heat so that the product assumes the shape of the mold and becomes a solid mass. This method of manufacturing pet chews does not solve the problem of mechanically manufacturing a substantially pure rawhide pet chew because it requires binders.
U.S. Pat. No. 4,702,929 to Lehn et al. (1987) discloses a method for processing rawhide or rawhide scraps which requires first dehydrating the wet scraps by a frame filter or piston press or by natural drying. After the scraps are dried, they are minced or ground into pieces as small as 3-6 mm. The ground rawhide scraps are then mixed with one or more binding materials, chosen from a group of starches, flours or grains. Coloring and flavoring additives may be added to the mix. The scrap/binder mixture is then extruded through a number of heating zones and then a die. Depending on the quality of the rawhide scrap, the resulting chew consists of 20-60 percent binder (see FIG. 2). However, Lehn et al. fails to disclose a process which results in a substantially pure rawhide treat, relying instead on the starch binders which the present invention avoids. Further, the drying and grinding steps are both energy and time consuming.
In contrast to the above discussed prior art, the present invention utilizes scrap rawhide, produces a substantially pure rawhide product without starch and other binders, allows the simple addition of flavors and colorings to the entire body of the pet chew and is energy and labor efficient.
The present invention is also capable of producing, through the use of two double screw extruders and a coextrusion die, a pet chew product which consists of a tube-like outer shell of substantially pure extruded rawhide filled with a soft filling, also made of substantially pure extruded rawhide. Because of the extraordinary nature of the inventive process, both the shell and the filling are free from fillers and will therefore last much longer than the previously available pet chews. In addition, additives and flavorings can be added separately to both the shell and the filling, in order to enhance the pet's enjoyment of the treat.